The present invention relates to a displacement fluid machine such as pumps, compressors or expansion machines.
Heretofore, there have been known, as a displacement type fluid machine, a reciprocating fluid machine, in which repeated reciprocation of a piston in a circular cylinder displaces a working fluid, a rotary type (rolling piston type) fluid machine, in which a cylindrical piston eccentrically rotates in a circular cylinder to displace a working fluid, and a scroll type fluid machine, in which a pair of stationary and orbiting scrolls with spiral laps arranged upright on end plates engage with each other to cause the swirl scroll to perform orbital movements to displace a working fluid.
The reciprocating fluid machine is advantageous in that it is simple in construction and so easy to manufacture and inexpensive. However, a stroke from the completion of suction to the completion of discharge is as short as 180 degrees in terms of a shaft rotating angle and so a flow rate is high during discharge stroke, resulting in a problem of degradation in performance due to increase in pressure loss. Further, in the reciprocating fluid machine, its rotary shaft system cannot completely be balanced since reciprocating motion of a piston is required, resulting in a problem of great vibration and noise.
Further, as compared with the reciprocating fluid machine, the rotary type fluid machine, in which a shaft rotating angle during a period from the completion of suction to the completion of discharge is as long as 360 degrees, is less problematic in an increased pressure loss during the discharge stroke but discharges once every shaft revolution to involve a relatively large variation in gas compression torque, which results in a problem of occurrence of vibrations and noises, as in the reciprocating fluid machine.
Further, having a shaft rotating angle of as large as 360 degrees or more (normally in the order of 900 degrees for ones practiced as air-conditioning use) during a period from the completion of suction to the completion of discharge, is greater than 360 degrees (that of those which have been practically used for air-conditioning is normally about 900 degrees), the scroll type fluid machine involves a less pressure loss during discharge stroke, and generally comprises a plurality of working chambers, so that variation in gas compression torque is small, and so vibrations and noises are low. However, since the management for a clearance between spiral laps in a lap engagement state, and for a clearance between laps and end plates is required, a process having a high degree of accuracy is required, and as a result, and accordingly, a problem of increasing the cost of the process. Further, since the shaft rotating angle during a period from the completion of suction to the completion of discharge is larger than 360 degrees so as to be too long, the time of stroke is long so as to raise a problem of increasing internal leakage.
By the way, Japanese Patent Unexamined Publication No. 55-23353 proposes a kind of displacement type fluid machine in which a displacer (orbiting piston) for displacing the working fluid revolves or orbits with a substantially constant radius without self-rotation, relative to a cylinder having been charged therein with the working fluid, in order to displace the working fluid. This proposed displacement fluid machine is composed of a piston having a petal shape in which a plurality of members (vanes) radially extending from the center of the piston, and a cylinder having a hollow portion which defines a gap equal to an orbit radius between the outer periphery of the piston and the inner periphery of the cylinder when the piston and the cylinder are set to be concentric with each other, the piston orbiting in the cylinder so as to displace the working fluid.
The displacement fluid machine disclosed in the Japanese Patent Unexamined Publication No. 55-23353 dose not have reciprocating portions as in the reciprocating fluid machine, and accordingly, the rotary shaft system can be completely balanced. Thus, this does not cause so much vibration, and further, the relative slipping speed between the piston and the cylinder is low so as to relatively decrease the frictional loss, that is, this machine has an advantage inherent to the displacement fluid machine.
However, the behavior of the piston is unstable during operation, and accordingly, it causes a problem of increased vibrations and noises and an increased leakage of the working fluid, which lead to degradation in performance.
Further, the passage area during suction stroke and discharge stroke, which is defined by a suction port and a discharge port in the compression working chamber, and the orbiting piston, varies depending upon a rotating angle of the shaft of the piston, and accordingly, it is hard to ensure the suction passage and the discharge passage which are necessary and sufficient, causing a problem of degraded performance.